According to the most conventional technique, a plate to be worked, for example for producing a top for a kitchen or bathroom cabinet, is cut starting from a plate of large dimensions on a machine that usually is dedicated only to the cutting operation (typically a bridge-like milling machine), after which the semi-finished product obtained thereby is usually transferred into a work centre of the type referred to above, to undergo subsequent milling, grinding, or polishing machining operations.
In the machine dedicated to the cutting operation, the plate to be cut is supported on a “sacrificial” supporting surface, typically defined by a board or frame made of wood or other sacrificial material, in such a way that the disk blade used in the cutting operation, passing through the plate, cuts the sacrificial supporting surface without interfering with the top surface of the bench of the machine. When the cut semi-finished product is transferred onto the numeric-control work centre, it is supported and held in a position that is raised with respect to the bench of the work centre by means of a plurality of supporting and holding blocks, which can be positioned as desired on the top surface of the bench of the work centre in such a way that machining operations on the plate, such as grinding and polishing of the lateral peripheral surface of the plate, can be performed by the working head without interfering with the bench of the work centre. According to the most usual technique, these supporting blocks each make use of a bottom suction cup and a top suction cup, which can be activated by vacuum to maintain in a desired position each block on the bench of the work centre and to maintain in a fixed position the plate supported on the block. Once again according to the usual technique, each supporting block constitutes an independent unit, which can be positioned as desired on the bench of the work centre. Each block is connected by means of hoses to a source of vacuum or it incorporates a vacuum source (see EP 2 682 227 A1 in the name of the present applicant).
The present applicant has early realized of the problem of providing a multi-functional work centre that is able to sum up in one and the same machine the specific capabilities of a bridge milling machine and those of a work centre. For instance, in Italian patent IT 1 391 863, the present applicant has proposed a work centre provided with a removable sacrificial supporting surface, which has a structure similar to that of a roller shutter, and which can be displaced between an operative position extended over the bench of the machine, when the work centre is to be used for carrying out cutting operations, and an inoperative rolled-up condition, where the bench of the work centre is left free for positioning thereon suction-cup supporting blocks adapted to receive thereon a plate that is to undergo milling or grinding machining operations. A further solution for a work centre with a removable sacrificial supporting surface has formed the subject of Italian patent IT 1 416 728 filed in the name of the present applicant. The aforesaid known solutions, however, lead to a relatively complicated structure and arrangement, which are not always justified.
Document No. DE 38 39 150 C1 describes a numeric-control work centre for machining plates of stone, marble, or, in general, natural or synthetic stone material, or ceramic material, comprising:                a work surface; and        at least one working head movable on the work surface in at least two mutually orthogonal horizontal directions, wherein the working head can be coupled either to a tool for performing grinding or milling machining operations on the plate or to a tool for cutting the plate,wherein said work surface includes:        a rigid supporting board, defining a first planar supporting surface; and        a series of elements for supporting a plate during a cutting operation, said elements being rigidly connected to said rigid supporting board and defining a second supporting surface located at a higher level than said first planar supporting surface of said supporting board, so that a cutting tool coupled to said at least one working head can carry out a cutting operation on a plate resting on said plate-supporting elements, without interfering with the supporting board,        
said machine including a third supporting surface located at a higher level than said second supporting surface, for supporting and holding a plate during a grinding or milling operation performed on the plate by using a tool coupled to said working head and suitable for performing grinding or milling machining operations on the plate.
As a result, the above known work centre is able to carry out both cutting operations and grinding or milling machining operations. However, it does not make use of sacrificial elements, and the cutting operations are considerably limited by the fact that the cutting tool can move with respect to the work surface only along orthogonal lines, within the free spaces between the elements that support the plate during the cutting operation.